It has been the common practice in four wheel drive type vehicles to use a central gear box, the output of which is fed directly to the individual driven wheels of a vehicle. However, in some applications, particularly where high ground clearance is required, it is desirable to have the drive shaft of each wheel come in at a position higher than the wheel spindle which causes problems with respect to driving the wheel. This problem is overcome by having the drive shaft connected to a pinion gear which is in mesh with an output gear normally splined to the wheel spindle. Due to the use of two gears at the wheel to allow for increased ground clearance, it is possible to reduce the size and gear reduction in the central gear box as some of this gearing is now taking place at the wheel. Although, a geared hub has proven more than satisfactory, in the field, it does introduce problems, particularly with respect to manufacturing of the device as well as the increased cost necessary to produce these units.
It has been the practice to manufacture a two piece gear hub to allow assembly of the gears within the casing and to allow casting of the various housing components. With geared hubs of this type, a high degree of machining is required to assure proper alignment of the casing components upon assembly. Particularly, the alignment of the wheel bearing apertures provided in each section of the housing for receiving wheel spindle has been difficult. Furthermore, these housings are normally vertically split to provide sufficient strength within the geared hub to withstand the forces exerted on the hub as the vehicle is driven over rough terrain. As can readily be appreciated, sealing of vertically split housings is difficult and oil leakage may become a problem. Furthermore, with vertically split housings, it is difficult to utilize the strength of both components to withstand the force exerted on the casing by a vehicle and therefore, one piece of the housing must be made substantially stronger to withstand these forces.
Assembly of split housings is also difficult, as care must be taken to assure the accurately machined abutting flanges of the housing do not warp due to improper bolt tightening procedures. Warping of these surfaces will result in oil leakage and normally cannot be corrected by reassembling the hub. Any misalignment of the plunger will result in excessive bearing wear and excessive gear wear which may or may not be detected when the unit is assembled. Severe misalignment can cause gear tooth breakage and may be detected due to high noise level when the unit is operated.
It can be appreciated that geared hubs are used for all terrain type vehicles and particularly military vehicles. Because of this application, the units must be reliable, inherently strong, require low maintenance and be relatively inexpensive to produce. The present invention mitigates the shortcomings of prior art systems by providing a one piece housing in which the entire unit cooperates to provide the required strength. Furthermore, because of the unique design, the geared hub is compact and can easily be assembled without the high machining costs of split housing arrangements. Furthermore, according to a preferred embodiment of the invention, the problems with respect to oil leaks is further reduced by providing an oil sump in the lower portion of the one piece housing such that the likelihood of leakage through abutting components is reduced.